1. Field of the Invention
The present invention relates to a circuit for a sensor which includes both an analog circuit and a digital circuit, a sensor circuit in which a sensor is added to the circuit, and a semiconductor device using the sensor circuit.
2. Description of the Related Art
A sensor is a kind of input device and has a function of converting physical quantities such as light, sound, temperature, magnetism, and pressure into electric signals (sensor signals). A sensor circuit includes the sensor and a circuit for processing sensor signals output from the sensor. Since the sensor signals output from the sensor are generally analog signals, the analog sensor signals need to be converted into digital signals before input to a signal processing circuit such as a microcomputer from the sensor circuit. Therefore, the circuit included in the sensor circuit can be classified into an analog circuit for processing analog sensor signals and a digital circuit for processing digital sensor signals.
A device for measuring physical quantities is disclosed in Patent Document 1; in the device, a detected analog signal is converted into a digital signal by an analog-to-digital converter circuit in accordance with a sampling pulse from a sampling circuit. A temperature detection device is disclosed in Patent Document 2; in the device, a voltage value of a signal flowing in a semiconductor element is held by a sample hold circuit and converted into a digital signal by an analog/digital (AD) converter circuit.